1. Field of the Invention
The present invention relates to a liquid droplet jetting apparatus which jets liquid droplets.
2. Description of the Related Art
In general, an ink-jet printer, which records images, letters and the like on a recording medium such as the printing paper, includes an ink-jet head (liquid droplet-jetting head) which has nozzles for jetting liquid droplets of the ink, and an ink cartridge (liquid storage container, ink tank) for storing the ink to be used for the ink-jet head. Usually, the ink-jet head and the ink cartridge are connected to one another by means of a tube made of resin. The ink, which is stored in the ink cartridge, is supplied to the ink-jet head via the tube.
In recent years, it is investigated that a plurality of ink-jet heads, which jet an ink of the same type (same color), are provided in one printer, for example, in order to improve the recording speed. When a plurality of ink cartridges are provided in the printer corresponding to the plurality of ink-jet heads respectively, then the number of the ink cartridges is increased, the cost is increased, and the printer is large-sized. Therefore, it is preferable that the ink can be simultaneously supplied from one ink cartridge to the plurality of ink-jet heads.
Japanese Patent Application Laid-open No. 10-95129 discloses an ink cartridge provided with two ink supply ports. The two ink supply ports of the ink cartridge are connected in parallel to two ink-jet heads by means of two supply-tubes (tubes). Therefore, it is possible to supply the ink of the same color to the two ink-jet heads respectively.
When one ink cartridge is connected to two ink-jet heads individually (in parallel) by means of a plurality of tubes, the total length of the tubes is consequently long as compared with a case in which one ink cartridge and two ink-jet heads are connected in series, which results in the increase in the cost. When the tubes are made of resin, and the tubes have the gas permeability to some extent, then the following problem may arise. That is, the ink contained in the tubes is dried little by little, and the viscosity is increased, and/or the bubbles make invasion into the tubes from the outside. In such a situation, the longer the total length of the tubes is, the larger the amount of the ink subjected to the increase in viscosity in the tubes is, and/or the larger the amount of bubbles to make invasion into the tubes is. If the viscosity-increased ink and/or the ink containing a large amount of bubbles is/are supplied to the ink-jet head, the jetting failure arises in the nozzle with ease. In view of the above, the present inventors have investigated that one ink cartridge and two ink-jet heads are connected in series in order to shorten the total length of the tubes.
However, when one ink cartridge and two ink-jet heads are connected in series, the length of the tubes, through which the ink pass until arrival at the most downstream head positioned at the most downstream side in the ink supply direction, is increased depending on the distance from the ink cartridge to the most downstream head. Therefore, the viscosity-increased ink and/or the ink containing a large amount of bubbles is/are supplied to the head which is disposed far from the ink cartridge. Therefore, the jetting failure tends to arise in the nozzles of the head which is separated far from the ink cartridge. It is necessary to frequently perform the recovery or restoring operation for recovering the jetting performance in order to remove the viscosity-increased ink, the bubbles, or the like, the recovery operation including the purge operation for forcibly discharging the ink from the nozzles.